This invention relates to dock levelers and in particular, a dock leveler which is used for loading and unloading rail cars. The invention specifically relates to a brake mechanism that prevents lateral movement of such a dock leveler when it is lowered into a working position.
Dock levelers are well known in the material handling field. These devices are typically used to span the distance between a loading dock and vehicle which is to be loaded or unloaded. One common use is to place a leveler in a pit or, at the edge of a loading dock and have it span the gap which exists between the edge of the loading dock and the bed of a truck which has been backed in for a loading and/or unloading. The leveler is stored in the pit, raised upward and then lowered so that the lip extends to provide the necessary bridge between the dock leveler and the truck bed. Since trucks are backed into discreet dock areas and are then secured by means of chocks, vehicle restraints, or the like their lateral position remains fixed. Thus, the position of the dock leveler is also fixed on its mounting frame and to the loading dock so that there is no lateral movement. Also since the truck typically backs up to within inches of the dock face it is very close to the loading dock surface.
A specialized use for dock levelers and, in particular, levelers which store vertically is to unload or load rail cars. It is this mode of utilization, the loading dock surface is disposed generally parallel the rails and there are no discreet docks as in the case of trucks. The rail car is moved into position for loading or unloading and then the vertically stored ramp is laterally placed into alignment with the rail car door. That is, the vertically stored ramp is generally itself movable on rails which are disposed parallel to those upon which the rail car moves. Movement of the dock leveler is also necessary because a rail car cannot generally be positioned with accuracy relative to a fixed point.
Thus, by mounting the leveler on rails additional utility is gained by having the leveler positionable anywhere along the loading dock to align with the door on the rail car. However, this functional requirement and flexibility also carries a disadvantage. When the dock leveler is lowered to the horizontal working position, the force exerted by fork-lift trucks which move over the ramp during loading or unloading can move the leveler sideward. Consequently, there exists in the technology a need to provide a technique for engaging and locking the dock leveler when it is lowered into a working position. Additionally, such a brake should automatically engage when the leveler is lowered into the operative position. Moreover, such a brake should be capable of adjustment so that the brake force can be varied. Finally, the braking force of such a device should remain essentially constant within the entire working range of the leveler.